This paper acquaints the reader with the psychopathology and psychodynamics of the sex murderer (and potential sex murderer), with an emphasis on treatment in an out-patient setting. Murder is a complex phenomenon with different clinical pictures, different etiologies and different prognoses. The authors review their system of classification based on the motivational dynamics of the act itself, and they detail the catathymic and compulsive murderer, which comprise the majority of most sexually motivated homicides. Three cases are presented that demonstrate: (1) a treatment failure due to the inability of the therapist to recognize important symptoms, (2) successful treatment of a catathymic sex murderer once released from custody and (3) successful treatment of a potential compulsive sex murderer.